1. Field of the Invention
The present invention relates to an electronic label and to a system for the contact-free identification of objects, notably metal objects such as for example gas cylinders.
To reference and identify such objects, there are known ways of affixing electronic labels to them. Such labels are each provided with a device for the reception and transmission of electromagnetic waves coupled with an electronic module enabling the processing of the signals received and the re-transmission of other signals comprising notably a message for the identification of the label and hence of the object to which it is affixed. Furthermore, the system has a reader comprising a device for the transmission/reception of electromagnetic waves to transmit information elements between a data terminal and said electronic label.
The reader fulfils several functions and is notably used to:
send the label the power needed for its operation, the label having no specific independent source of power, PA1 send the label data elements coming from the terminals, these data elements being possibly capable of being recorded in a memory with which the label is provided, PA1 receive data elements that come from the label and are specific to this label, notably in order to identify this label. PA1 a label comprising a coil with an axis, and PA1 a reader having one or more transmission/reception devices offset in angular fashion about a median axis, each transmission/reception device of the reader comprising two substantially parallel bars on which there are respectively wound two coils having respective ends located substantially in one and the same plane and forming two poles that are substantially parallel and located in said plane, substantially parallel to said axis, in a configuration such that the field generated has opposite orientations in the two bars so that at least a part of the lines of said magnetic field can get looped in the magnetic circuit in passing into the coil of the label along the direction of the axis of said coil when the reader is placed in the vicinity of said label. PA1 a layer of insulator material placed at the bottom of the protective cup around the control valve, PA1 an electronic module associated with an antenna comprising a coil wound on a ferrite rod, the antenna being fixed to the layer, parallel to the surface of this layer, and PA1 a first foil made of a material that is a conductor of magnetic fields and has a low coercive field, this foil extending above the antenna.
To carry out these various operations of transmission, the transmission/reception device of the reader has an antenna, formed for example by a coil with a ferrite core. This antenna is used for transmission and reception.
The label too has an antenna for the reception of the electromagnetic waves sent by the reader, the same antenna being used also to transmit data elements to the reader. In reception mode, the antenna is a means of reception by induction of the power coming from the reader, as well as a means of reception of the data sent out by this reader. The antenna is connected to an electronic circuit, for example an electronic chip, comprising the means needed to demodulate the signals received by the antenna, decode these signals and store them, as well as to encode and modulate the signals to be re-transmitted.
A major problem of these systems is that of enabling the label to receive the power needed for its operation with maximum efficiency so as to make it possible to reduce the power of the electromagnetic radiation sent out by the reader and limit the space requirement of the antennas and enable transmission of the power and signals without undergoing the constraint of an excessively short transmission distance.
2. Description of the Prior Art
In an attempt to resolve this problem, it has already been proposed to make a label antenna of the ferrite container type, formed by a cylindrical ferrite element having, on one of its plane faces, a ring-shaped groove within which a coil is housed. Such an antenna is necessarily fixed to the object to be identified, with its axis perpendicular to the surface of the object. Owing to the relatively great height of the ferrite container, this antenna takes up space in a cumbersome way in the axial direction. To overcome this problem, there is a known way of embedding the label on the surface of the object. For example, there is a known way of placing labels of this type in a housing hollowed out in the knob of the control valve of a gas cylinder. Therefore, the antenna is necessarily small-sized.
The antenna of the reader is made similarly by means of a coil whose axis has to be placed substantially in the direction of the axis of the antenna of the label in order to provide for the most efficient power transmission possible. To increase the efficiency, reasons related to the availability of space make it impossible in practice to implement the approach wherein the diametrical dimension of the antenna of the label is increased to pick up more of the flux lines sent by the reader. It has thus proved to be the case that the distance between the reader and the label can hardly exceed 5 mm with such a system.
Another approach envisaged is that of making the antenna of the label in the form of a coil surrounding an elongated ferrite rod, for example with a length of 15 mm and a diameter of 3 mm.
In order that the flux lines of the magnetic field may flow in the ferrite rod in the axial direction of the coil, this coil must be in a position that is substantially parallel to the surface of the object to which the label is affixed. A first drawback of this arrangement is that, in order to enable the transmission of power and data between a reader of the above type and the label, the antenna of the reader must be oriented so that its axis is pointed substantially in the axial direction of the coil of the antenna of the label. The result thereof is that it is impossible to read the label in a sure way without taking care over the relative orientation of this label with respect to the reader. Furthermore, the label needs to be placed in a position where it is mechanically protected. In the case of gas cylinders, this is done by placing the label in the vicinity of the control valve, within the protective cup of this control valve, in a plane substantially perpendicular to the axis of the cylinder. To provide for the efficient transmission of power between the reader and the antenna of the label, it would be necessary to place the antenna of the reader in an axial alignment with the antenna of the label. This is practically impossible within the cup for reasons of space, and if the reader is placed outside the cup, the latter forms a screen that greatly disturbs transmission.
Consequently, although labels with ferrite rod type antennas have certain advantages notably in terms of space requirements, there are many objects, notably gas cylinders, on which these labels, when affixed thereto, cannot be read reliably and easily by means of a reader provided with a standard antenna.
In order to overcome the above problems and enable a reliable identification of objects provided with electronic labels while, at the same time, limiting the constraints related to the reading of these labels, the inventor has already developed an approach consisting of the use of:
This system has the advantage wherein, with the two coils being wound so that a magnetic flux is created from one coil to the other in flowing through the coil of the label, the power transmitted and the sensitivity of reception are practically doubled.
Through this system, it is possible to achieve the reliable reading of an electronic label comprising a ferrite rod type antenna placed in a parallel position against or close to the surface of an object provided that the reader can be brought to the vicinity of this surface, substantially perpendicularly to this surface. Hence, through this system, it is possible to read such an electronic label in a reliable way even when protection means surround the label, as is the case for example for gas cylinders with protective cups.
The inventor has also proposed an electronic label comprising a foil made of electrically conductive non-magnetic metal alloy, the antenna extending to the direct vicinity of the foil, the axis of the coil being parallel to this foil.
Indeed, during the reading of a label having an antenna formed by a coil wound around a ferrite rod placed in a position that is parallel to the surface of the object, the magnetic flux emitted by the reader goes partly beside the antenna, in forming a leakage flux despite the flux-concentrating capacity of the ferrite rod. Depending on the nature of the material of the object, this leakage flux may be substantially modified, thereby disturbing the flux that flows through the ferrite rod. Thus, for example, if the object is made of magnetic material, for example steel, a major part of the flux emitted will flow into this material to the detriment of that part of the flux which goes through the ferrite of the label. Conversely, if the material of the object is non-magnetic, it acts as a reflector for the magnetic field, the reflected field lines disturbing the emitted field in the vicinity of the antenna. There may even be the risk of that these field lines will create by interference field nodes where the field gets cancelled. Consequently, the power received by the label and the general behavior of this label are variable as a function of the constituent material of the object. This gives rise to variations in reading conditions and notably variations in the acceptable distance between the reader and the label.
The above-defined label makes it possible to overcome this problem by making the behavior of the label independent of the nature of the support to which it is affixed, the foil of non-magnetic conductive material fulfilling the role of a screen that always acts in the same way whatever may be the underlying material.
The invention is aimed at improving the above label and system and at enabling a surer identification of objects provided with electronic labels while at the same time limiting the constraints related to the reading of these labels.